1. Field of the Invention
This invention relates to an apparatus for continuously taking off a thermoplastic synthetic resin sheet material foamed by a vertical foaming furnace.
2. Prior Art
A foamed synthetic resin sheet produced by a vertical foaming furnace caused longitudinal wavy wrinkles. The wrinkles occurred when foaming. Accordingly, in order to remove the wrinkles, it is known to laterally orient a foamed sheet.
Japanese Patent Publication No. 48-9955 discloses an apparatus for taking off a polyolefin synthetic resin sheet foamed by a vertical foaming furnace The apparatus comprises a pair of rotary suction belts (made of cloth or rubber belts in which a number of fine holes are perforated) having a number of vent holes, and a vacuum suction device. The rotary suction belts are provided at an interval set by considering a distance corresponding to a rate of lateral expansion of the foamed sheet oppositely in a symmetrical manner. The belts suck air through the vent holes to suck both ends of the foamed sheet in its lateral direction, thereby orienting the sheet.
In the apparatus as described above, the thermoplastic synthetic resin sheet heated and foamed by the vertical foaming furnace is continuously taken off by the suction belts immediately after heating and foaming. In this taking off method, its suction force has a limit so that the holding force of the suction belts for the sheet is weak. Thus, the above method has the following disadvantages.
(1) The sheet material cannot be held to the suction belts by the suction force against the fluctuation of the sheet or the irregular thickness of the sheet due to variations in hot blast stream in the hot blast in the foaming furnace. PA1 (2) When a thin sheet or the sheet having a weak film strength is employed, the sucked portion of the film is broken by its suction force so that the sheet cannot be held. If the suction force is weakened so as to prevent the sheet from breaking, the sheet cannot be held because the suction force cannot hold the sheet due to the weight of the sheet. PA1 (3) When the falling speed of the sheet from the foaming furnace is slow or the taking-off speed of the apparatus is slow, the sheet cannot be held by the belts due to the weight of the sheet similarly to the case of the above paragraph (2). PA1 (4) The sheet is fusion-bonded to the suction belts due to the slight temperature rise of the foaming furnace, and the sheet cannot be exfoliated from the belts. The sheet becomes hard due to the slight temperature fall of the foaming furnace, and the sheet cannot be sucked to the belts.